Drug trial reliability queried

22:05, Oct 15 2011
The Therapeutics Initiative at the University of British Columbia is concerned by gaps in the published data on Pradaxa.

A Canadian drug safety monitoring group has cast doubt on the reliability of trials of the new blood-thinning drug causing problems in New Zealand, and is calling for further studies before the medicine can be declared safe.

The Therapeutics Initiative at the University of British Columbia is concerned by gaps in the published data on Pradaxa and an apparent increase in heart attack rates among patients. It says licensing the 150mg dose of the drug for heart rhythm disorder is "premature, pharmalogically irrational and unsafe for many patients".

The Australian government has delayed introducing Pradaxa because of concerns around potential cost blow-outs and the drug's efficacy.

A Sunday Star-Times investigation has revealed concerns about Pradaxa, also known by the generic name dabigatran, after dozens of adverse reactions among mostly elderly patients, including serious bleeds and gastro-intestinal problems. A coroner is investigating reports of seven deaths associated with the drug.

Pharmac, which described Pradaxa as a "game changer" when it announced in July that it was funding the drug in a deal worth up to $155 million over five years, now says that if patients are well controlled on the standard blood-thinner warfarin, there is "no reason to change".

Pharmac's medical director Peter Moodie moved to assuage fears about Pradaxa, saying the "intense coverage" by the Star-Times had focused on side effects that were already known.


"We have a particular concern that the media coverage may cause patients to stop taking an important medicine without first seeking advice from their doctor. It is very important that if you are taking blood thinner medicine, you do not stop this without first discussing it with your doctor," Moodie said.

He said 122 cases had been reported to the Centre for Adverse Reactions Monitoring (CARM), of which two out of five involved bleeding. As of a month ago, CARM had been alerted to four deaths, none of which were directly caused by Pradaxa. "We are aware of nine patients who may have suffered avoidable bleeds, mainly because the drug was introduced too quickly after stopping warfarin or because their kidney function was not adequate," he said.

Moodie said Pradaxa could cause more bleeding from the bowel than warfarin, but fewer brain bleeds and those risks and benefits needed to be weighed up with a patient's doctor.

He said the reported side effects of Pradaxa were in line with those reported for any new medicine.

"What is unusual is the intense attention that has been given to this medicine. While all reports of harm are worrying and need to be monitored carefully, it is important to realise that more than 7000 patients are known to have taken the medicine in New Zealand."

Moodie cited an international study of 18,000 patients as evidence of Pradaxa's safety.

But questions remain about the study, after the Food and Drug Administration in the US asked its authors to re-evaluate their database for possible under-reporting of adverse events, prior to granting approval to the drug.

The re-analysis found scores of previously unidentified adverse events including strokes, major bleeding and heart attacks. The investigators who ran the trial said the missed events were not unexpected for a study of that size and did not lead to any changes in the results.

But Aaron Tejani, of the Therapeutics Initiative, told online news service heartwire that not knowing the total serious adverse events made it impossible to gauge the full clinical impact of Pradaxa relative to warfarin in the trial, and therefore to adequately appreciate the drug's risks.

Tejani told the Star-Times the company that made Pradaxa, Boehringer Ingelheim, needed to provide the "full data set, and have an independent group analyse that". Another double-blinded trial should be run to see if the findings of the original study could be replicated and to get more information on the signal of increased heart attacks. The optimal dose of Pradaxa for the heart rhythm disorder atrial fibrillation was also unclear, he said.

Sunday Star Times